Semiconductor diodes are useful in a number of electronic applications. A non-linear response characteristic of such diodes provides for applications in rectification of electrical wave forms. Additionally, the non-linear response characteristic of diodes provides for clipping or limiting of such wave forms. The non-linear response characteristic of diodes further provides for waveform sampling and frequency mixing applications.
In general, the non-linear response characteristic of semiconductor diodes is dependent on a voltage applied thereto. For example a forward bias voltage applied to a semiconductor diode provides for forward conduction through the diode. In contrast, a reverse bias voltage applied to the semiconductor diode substantially prevents reverse conduction through the diode.
A popular type of semiconductor diode is known as a p-n junction diode. A p-n junction diode often comprises a single semiconductor material that includes two differently doped regions. A first one the regions is doped with p-type impurity so that holes are majority carriers of current flow therethrough and electrons are minority carriers. A second one of the regions is doped with n-type impurity so that electrons are majority carriers of current flow therethrough and holes are minority carriers. The two regions contact each other at a p-n junction.
A "switching time" or "recovery time" in which the diode is switched from the forward conduction to the reverse conduction is important in the diode applications discussed previously herein. In p-n junction diodes such switching time or recovery time is substantially limited by behavior of minority carriers in p-n junction diodes, as discussed for example in Physics of Semiconductor Devices, Chapter 2: p-n Junction diode, by S. M. Sze, pages 63-132, John Wiley (1981). A particularly helpful discussion of such limitations is found in section 2.6.1 of Chapter 2 of Sze, pages 108-111, which is incorporated herein by reference.
Various methods have been used to provide decreased recovery time in p-n junction diodes. So called "fast recovery diodes" are discussed in section 2.7.5 of Chapter 2 of Sze (page 116 incorporated by reference). In fast recovery diodes, minority carrier lifetime in the junction is reduced by introducing recombination centers, thereby reducing recovery time. For example, by introducing Gold recombination centers into Silicon semiconductor diodes, recovery times in a range of 1 to 5 nanoseconds are achieved. By introducing suitable recombination centers into GaAs semiconductor diodes, recovery times on the order of 0.1 nanoseconds are achieved.
Unfortunately, it is not possible to reduce recovery times to zero by introducing an extremely large number of recombination centers, because a reverse generation current of a p-n junction is proportional to the number of recombination centers. Accordingly, while introduction of recombination centers provides some limited improvement in recovery time, an alternative is desirable. Furthermore, while experimental devices operating at cryogenic temperatures provide some interesting effects, equipment needed to maintain such temperatures adds undesirable burdens. What is need is a semiconductor diode that provides a reduced recovery time, at room temperature, independent of any minority carrier recombination.